in modern society, in a high-speed 4G network, a voice solution mainly includes a Circuit Switched Domain Fallback (CSFB) solution, which mainly falls back to a Global System for Mobile Communications (GSM) or a Wideband Code Division Multiple Access (WCDMA) network to support a Circuit Switched (CS) service. However, a mobile terminal cannot register on a network in a call process or is out of service, thus bringing a poor experience for a user.